Abstract: Objective To explore the interaction between P311 and transforming growth factor beta 1 (TGF-β₁) in murine fibroblasts and its effect on the function of fibroblasts. Methods Skin fibroblasts obtained from five neonatal P311 wild-type C57BL/6 mice and P311 gene knock-out C57BL/6 mice were cultured. The second passage of fibroblasts were used in the following experiments. All experiments were repeated for 3 times. (1) The fibroblasts of P311 wild-type mice were divided into blank control group and P311 over-expression group according to the random number table (the same grouping method below), with 36 wells in each group. Fibroblasts in blank control group were transfected with 10 μL control vector, and fibroblasts in P311 over-expression group were transfected with equal efficiency P311 expression adenovirus vector. After being cultured for 48 hours, the mRNA expression level of P311, and the mRNA and protein expression levels of TGF-β₁, α-smooth muscle actin (α-SMA), and collagen type Ⅰ of fibroblasts in both groups were determined with real-time fluorescent quantitative RT-PCR and Western blotting (the same detection methods below), respectively. (2) After cultured reaching the cell density of 80%-90%, the mRNA and protein expression levels of TGF-β₁, α-SMA, and collagen type Ⅰ of the fibroblasts of P311 wild-type mice and P311 gene knock-out mice, with 4 flasks in each type of fibroblasts, were determined. (3) The fibroblasts of P311 wild-type mice were divided into blank control group and 5, 10, 15, 20, and 25 ng/mL TGF-β₁ groups after being starved treatment with DMEM medium containing 1% FBS for 3 hours, with 2 flasks in each group. Fibroblasts in blank control group were routinely cultured, while fibroblasts in the latter five groups were treated with 5, 10, 15, 20, and 25 ng/mL TGF-β₁, respectively. After being cultured for 48 hours, the mRNA expression levels of P311 in fibroblasts of the six groups were determined. Another fibroblasts of P311 wild-type mice were divided into blank control group and 10 ng/mL TGF-β₁ group, with 6 wells in each group, and the protein expression levels of P311 in both groups were determined by immunofluorescence staining. (4) The fibroblasts of P311 wild-type mice were divided into blank control group and 10 ng/mL TGF-β₁ group after being starved treatment as above, with 2 flasks in each group, and fibroblasts in blank control group were routinely cultured, while fibroblasts in the latter group were treated with 10 ng/mL TGF-β₁. After being cultured for 48 hours, the mRNA and protein expression levels of α-SMA and collagen type Ⅰ were determined. The fibroblasts of P311 gene knock-out mice were grouped and treated as above, and the mRNA and protein expression levels of α-SMA and collagen type Ⅰ were determined. Data were processed with one-way analysis of variance and t test. Results (1) The mRNA expression level of P311 of fibroblasts in P311 over-expression group was increased nearly 300 000-fold compared with that in blank control group (t=9.942, P<0.001). The mRNA expression levels of TGF-β₁, α-SMA, and collagen type Ⅰ of fibroblasts in P311 over-expression group, and the protein expression levels of pro-TGF-β₁, activated TGF-β₁, α-SMA, and collagen type Ⅰ of fibroblasts in P311 over-expression group were significantly higher than those in blank control group (with t values from 8.192 to 49.090, P values below 0.01). (2) The mRNA expression levels of TGF-β₁, α-SMA, and collagen type Ⅰ in fibroblasts of P311gene knock-out mice were significantly lower than those in fibroblasts of P311 wild-type mice (with t values from 8.157 to 22.270, P values below 0.01). The protein expression levels of pro-TGF-β₁, α-SMA, and collagen type Ⅰ in fibroblasts of P311 gene knock-out mice were significantly lower than those in fibroblasts of P311 wild-type mice (with t values from 2.995 to 12.600, P<0.05 or P<0.01), and the protein expression levels of active TGF-β₁ were similar in two types of fibroblasts (t=1.070, P>0.05). (3) The mRNA expression levels of P311 of fibroblasts in blank control group and 5, 10, 15, 20 and 25 ng/mL TGF-β₁ groups were 1.28±0.44, 3.61±0.91, 6.64±0.92, 6.58±1.04, 1.79±0.31, 0.16±0.06, respectively. Compared to the mRNA expression level of P311 of fibroblasts in the blank control group, the mRNA expression levels of P311 of fibroblasts in 5 and 20 ng/mL TGF-β₁ groups were similar (with t values respectively 2.302 and 0.955, P values above 0.05), while they were significantly higher in 10 and 15 ng/mL TGF-β₁ groups (with t values respectively 5.630 and 4.710, P values below 0.001), and they were significantly lower in 25 ng/mL TGF-β₁ group (t=2.509, P<0.01). The protein expression level of P311 of fibroblasts in 10 ng/mL group was higher than that in blank control group. (4) The mRNA and protein expression levels of α-SMA and collagen type Ⅰ of fibroblasts of P311 wild-type mice in 10 ng/mL TGF-β₁ group were significantly higher than those in blank control group (with t values from 3.523 to 14.290, P<0.05 or P<0.01). The mRNA and protein expression levels of α-SMA and collagen type I of fibroblasts of P311 gene knock-out mice in 10 ng/mL TGF-β₁ group were significantly higher than those in blank control group (with t values from 4.895 to 14.870, P<0.05 or P<0.01). Conclusions The interaction between P311 and TGF-β₁ in murine fibroblasts exists and it may enhance the differentiation of fibroblasts in combination.